The present technology relates to a driving device that drives a light-emitting element, and a light-emitting unit that includes such a driving device, and more specifically to a driving device that is well-suited for driving a surface-emitting type semiconductor laser, and a light-emitting unit that includes such a driving device.
In the field of a laser printer, to meet the demand for higher-speed performance and higher-density mounting, it has been taken into consideration to achieve higher-speed performance and higher-density mounting of a surface-emitting type semiconductor laser (hereinafter simply called a “surface-emitting laser”). However, the surface-emitting laser may have a light-emission resistance of nearly about 100 ohms that is larger by an order of magnitude as compared with an edge-emitting type semiconductor laser (hereinafter simply called an “edge-emitting laser”), as well as a larger parasitic capacitance that may be increased due to a multichannel configuration. In addition, the light-emission resistance of the surface-emitting laser may vary due to any change in temperature that could be caused by light emission, resulting in variation in the light-emission characteristics.
Consequently, in the surface-emitting laser, stabilization of the light-emission characteristics has been often attempted using a current driving method instead of a voltage driving method that could be influenced by variation in the light-emission resistance (for example, see Japanese Unexamined Patent Application Publication No. S57-13790). In the surface-emitting laser, however, the rising characteristics (TR characteristics) and the falling characteristics (TF characteristics) that are not significantly influenced in the edge-emitting laser may depend on a time constant that is determined by the light-emission resistance and parasitic capacitance. In the current driving method, therefore, a waveform of a driving signal for driving the surface-emitting laser would lose steep rising/falling edges.